Particles on your critical components can impact performance of the final product or the next step in the build process. The goal must be to minimize particulates. Monitoring for particles is important but may not uncover the root causes. Taking a detective approach and thoroughly investigating the “crime” scene can uncover particle sources you may not have thought of (see diagram) and either solve recurrent production problems or head-off problems before they start.

PROCESS ENVIRONMENT
Particles can come from the surrounding environment. This includes the air, personnel, and process chemicals, including water. Cleanroom procedures and maintenance programs are important, but they must be appropriately designed and executed. We see examples of significant particle contamination in what appear initially to be well-maintained cleanrooms and experienced, educated personnel who understood the requirements.

When companies move to a new location, the provenance or history of the room may not be known. In one case, the company inherited a cleanroom from a previous tenant. There were no records of when filters had been installed. Periodic air particle counting and airflow pressure monitoring indicated that particle levels were acceptable for the application. However, the change in ownership and the loss of data made validation and maintenance rather problematic. Even though there were no immediate particle problems, the next recommended step was a thorough and formal inspection of the filters and of the overall cleanroom design.

The problem was solved by using the principle that Toyota Motor Corporation calls Genchi Genbutsu or “go to the source.”¹ In another example, a cleanroom appeared to be appropriately designed; gowning and cleanroom protocols were carefully followed. However, periodic high particle count spikes were observed.During a visit to the cleanroom plenum, we determined that air ducts had not been cleaned; gaskets were worn; and the selected filters were, to say the least, not optimal for the performance requirements. Excessive particles had accumulated and were bypassing filters. The filters had been replaced according to schedule, but there was an air route around the filter. Therefore, filter clogging was not detected by pressure monitoring. In addition, in collaborating with the facilities group, we determined that environmental issues and nearby construction probably exacerbated the level of incoming particles. In this case Genchi Genbutsu involved observing the insides of ducts, inspecting filters, and working with personnel closer to the source of the problem.